Exploring future applications of the apiculate yeast Hanseniaspora.

As a metaphor, lemons get a bad rap; however the proverb 'if life gives you lemons, make lemonade' is often used in a motivational context. The same could be said of Hanseniaspora in winemaking. Despite its predominance in vineyards and grape must, this lemon-shaped yeast is underappreciated in terms of its contribution to the overall sensory profile of fine wine. Species belonging to this apiculate yeast are known for being common isolates not just on grape berries, but on many other fruits. They play a critical role in the early stages of a fermentation and can influence the quality of the final product. Their deliberate addition within mixed-culture fermentations shows promise in adding to the complexity of a wine and thus provide sensorial benefits. Hanseniaspora species are also key participants in the fermentations of a variety of other foodstuffs ranging from chocolate to apple cider. Outside of their role in fermentation, Hanseniaspora species have attractive biotechnological possibilities as revealed through studies on biocontrol potential, use as a whole-cell biocatalyst and important interactions with Drosophila flies. The growing amount of 'omics data on Hanseniaspora is revealing interesting features of the genus that sets it apart from the other Ascomycetes. This review collates the fields of research conducted on this apiculate yeast genus.

PCR-based gene targeting in Hanseniaspora uvarum.

Lack of gene-function analyses tools limits studying the biology of Hanseniaspora uvarum, one of the most abundant yeasts on grapes and in must. We investigated a rapid PCR-based gene targeting approach for one-step gene replacement in this diploid yeast. To this end, we generated and validated two synthetic antibiotic resistance genes, pFA-hygXL and pFA-clnXL, providing resistance against hygromycin and nourseothricin, respectively, for use with H. uvarum. Addition of short flanking-homology regions of 56-80 bp to these selection markers via PCR was sufficient to promote gene targeting. We report here the deletion of the H. uvarum LEU2 and LYS2 genes with these marker genes via two rounds of consecutive transformations, each resulting in the generation of auxotrophic strains (leu2/leu2; lys2/lys2). The hereby constructed leucine auxotrophic leu2/leu2 strain was subsequently complemented in a targeted manner, thereby further validating this approach. PCR-based gene targeting in H. uvarum was less efficient than in Saccharomyces cerevisiae. However, this approach, combined with the availability of two marker genes, provides essential tools for directed gene manipulations in H. uvarum.

The Influence of Pichia kluyveri Addition on the Aroma Profile of a Kombucha Tea Fermentation.

Traditional kombucha is a functional tea-based drink that has gained attention as a low or non-alcoholic beverage. The fermentation is conducted by a community of different microorganisms, collectively called SCOBY (Symbiotic Culture of Bacteria and Yeast) and typically consists of different acetic acid bacteria and fermenting yeast, and in some cases lactic acid bacteria that would convert the sugars into organic acids-mostly acetic acid. In this study, the effect of including a Pichia kluyveri starter culture in a kombucha fermentation was investigated. P. kluyveri additions led to a quicker accumulation of acetic acid along with the production of several acetate esters including isoamyl acetate and 2-phenethyl acetate. A subsequent tasting also noted a significant increase in the fruitiness of the kombucha. The significant contribution to the aroma content shows the promise of this yeast in future microbial formulations for kombucha fermentations.

The film-forming Pichia spp. in a winemaker's toolbox: A simple isolation procedure and their performance in a mixed-culture fermentation of Vitis vinifera L. cv. Gewürztraminer must.

Certain yeast species belonging to the Pichia genus are known to form a distinctive film on grape must and wine. In a mixed-culture type fermentation, Pichia spp. (P. kluyveri in particular) are known to impart beneficial oenological attributes. In this study, we report on an easy isolation method of Pichia spp. from grape must by exploiting their film-forming capacity on media containing 10% ethanol. We isolated and identified two Pichia species, namely Pichia kudriavzevii and Pichia kluyveri, and subsequently co-inoculated them with Saccharomyces cerevisiae to ferment Gewürztraminer musts. Noteworthy differences included a significant increase in the 2-phenethyl acetate levels with the P. kluyveri co-fermentation and a general increase in ethyl esters with the P. kudriavzevii co-fermentation. Both Pichia co-inoculations yielded higher levels of glycerol in the final wines. Based on all the wine parameters we tested, the P. kluyveri strain that was isolated performed similarly to a commercial P. kluyveri strain.

Microbial Degradation of 2-Methylisoborneol in Forest Soil.

Microorganisms use a complex array of chemical compounds to interact with their surroundings. They produce and process different molecules in response to changes in the environment or in their metabolism. One of the most well-known volatile organic compounds produced by microorganisms is the C11-terpenoid 2-methylisoborneol (2-MIB), which has received attention because of the off-flavor it confers to fresh and reservoir water as well as to cultured fish. Cleaning water supplies of the off-flavor 2-MIB has been of interest for the scientific community for years, with the use of techniques that are either expensive, e. g., activated carbon, or create toxic byproducts, e. g., ozonation. In the present study, soil samples from nature were collected from a forest and the volatile organic compounds produced by microbes were extracted and analyzed with focus on non-canonical terpenoid structures. HS-SPME-GC/MS analysis of soil samples revealed 1-methylcamphene (1-MC), 2-methylenebornane (2-MB) and 2-MIB as C11-terpenoids. Due to the high 1-MC/2-MIB ratio compared to previous reports, it was hypothesized that microbial degradation of 2-MIB was in place. Addition of synthetic 2-MIB to biologically active soil revealed complete degradation of the pollutant to 2-MB, 1-MC and 2-methyl-2-bornene (2-M2B). The results suggest the potential of using respective natural microorganisms for biodegradation of 2-MIB, with applications in water treatment, fishery and soil ecology.

Construction and Analysis of a Yeast for the Simultaneous Release and Esterification of the Varietal Thiol 3-Sulfanylhexan-1-ol.

Polyfunctional thiols like 3-sulfanylhexan-1-ol (3SH) and its ester 3-sulfanylhexyl acetate (3SHA) are important aroma determinants in wine with exceptionally low odor thresholds. 3SH is largely found in grape must bound to glutathione and cysteine and requires enzymatic action to be perceived sensorially. The wine yeast Saccharomyces cerevisiae is ineffective in releasing volatile thiols from their precursor configuration. For this purpose, a yeast strain was constructed that expresses the carbon-sulfur lyase encoding the tnaA gene from Escherichia coli and overexpresses its native alcohol acetyltransferase encoding genes, ATF1 and ATF2. The resulting yeast strain, which co-expresses tnaA and ATF1, showed elevated 3SH-releasing capabilities and the esterification of 3SH to its acetate ester 3SHA. Levels of over 7000 ng/L of 3SHA in Sauvignon blanc wines were achieved. Enhanced release and esterification of 3SH were also shown in the fermentation of guava and passionfruit pulp and three hop varieties. This study offers prospects for the development of flavor-enhancing yeast strains with optimized thiol-releasing and esterification capabilities in a diverse set of beverage matrices.

Development of Genetic Modification Tools for Hanseniasporauvarum.

Apiculate yeasts belonging to the genus Hanseniaspora are commonly isolated from viticultural settings and often dominate the initial stages of grape must fermentations. Although considered spoilage yeasts, they are now increasingly becoming the focus of research, with several whole-genome sequencing studies published in recent years. However, tools for their molecular genetic manipulation are still lacking. Here, we report the development of a tool for the genetic modification of Hanseniaspora uvarum. This was employed for the disruption of the HuATF1 gene, which encodes a putative alcohol acetyltransferase involved in acetate ester formation. We generated a synthetic marker gene consisting of the HuTEF1 promoter controlling a hygromycin resistance open reading frame (ORF). This new marker gene was used in disruption cassettes containing long-flanking (1000 bp) homology regions to the target locus. By increasing the antibiotic concentration, transformants were obtained in which both alleles of the putative HuATF1 gene were deleted in a diploid H. uvarum strain. Phenotypic characterisation including fermentation in Müller-Thurgau must showed that the null mutant produced significantly less acetate ester, particularly ethyl acetate. This study marks the first steps in the development of gene modification tools and paves the road for functional gene analyses of this yeast.

Effect of Isomixing on Grape Must Fermentations of ATF1-Overexpressing Wine Yeast Strains.

Speeding up grape must fermentation would be of great economic benefit. We subjected Saccharomyces cerevisiae VIN13 and two recombinant VIN13-strains expressing ATF1 alleles under two different promoters (either PGK1 or HXT7) to four styles of grape must fermentations; we then assessed the effect of constantly stirring a must fermentation (isomixing). The four different fermentation setups were as follows: isomixed, closed in an ANKOM Rf Gas productions system; isomixed, open in a stirred tall tube cylinder; static, closed constituting a conventional fermentation in a wine bottle equipped with an airlock and static; and static, open in a tall tube cylinder (without stirring). We report on major fermentation parameters and the volatile aroma compositions generated in the finished wines. The primary fermentations of the strains subjected to constant stirring finished after 7 days, whereas the static fermentations reached dryness after 19 days. The wines derived from isomixed fermentations produced approximately 0.7% less ethanol compared to the unstirred fermentations. The speed that the isomixed fermentation took to reach completion may provide an alternative to static fermentations in the preparation of base wines for sparkling wine production. The observed increase of volatiles of isomixed fermentations merits further investigation.

Blending wine yeast phenotypes with the aid of CRISPR DNA editing technologies.

In recent years, CRISPR/Cas9-based genetic editing has become a mainstay in many laboratories including manipulations done with yeast. We utilized this technique to generate a self-cloned wine yeast strain that overexpresses two genes of oenological relevance i.e. the glycerol-3-phosphate dehydrogenase 1 (GPD1) and the alcohol acetyltransferase 1 (ATF1) directly implicated in glycerol and acetate ester production respectively. Riesling wine made from the resulting strain showed increased glycerol and acetate ester levels compared to the parental strain. In addition, significantly less acetic acid levels were measured in wine made with yeast containing both genetic alterations compared to wine made with the strain that only overexpresses GPD1. Thus, this strain provides an alternative strategy for alleviating the accumulation of acetic acid once glycerol production is favoured during alcoholic fermentation with the addition of dramatically increasing acetate esters production.

The Whiff of Wine Yeast Innovation: Strategies for Enhancing Aroma Production by Yeast during Wine Fermentation.

Despite being used chiefly for fermenting the sugars of grape must to alcohol, wine yeasts (most prominently Saccharomyces cerevisiae) play a pivotal role in the final aroma profiles of wines. Strain selection, intentionally incorporating non-Saccharomyces yeast in so-called mixed-culture fermentations, and genetic modifications of S. cerevisiae have all been shown to greatly enhance the chemical composition and sensory profile of wines. In this Review, we highlight how wine researchers employ fermenting yeasts to expand on the aroma profiles of the wines they study.

Bioflavour Conference 2018-Biotechnology for Flavors, Fragrances, and Functional Ingredients.

The "Bioflavour 2018-Biotechnology of Flavors, Fragrances, and Functional Ingredients" conference was held from September 18th to 21st, 2018 at the DECHEMA house in Frankfurt, Germany. The conference attracted more than 190 participants from over 25 countries, with about 40% share from industry. Particular sessions of Bioflavour 2018 focused on "flavor perception and biotechnology", "microbial cell factories", "novel pathways, enzymes, and biocatalysts", "technological and regulatory aspects of flavor and fragrance biotechnology", "advanced analytics and novel compounds", "plant biosynthesis and plant enzymes", "modern biotechnology in the world of wine", "receptors, flavors, and bioactives", and "bioprocess development and downstream processing". At Bioflavour 2018, both cutting-edge science from renowned academic research groups and current innovation from this modern biotechnology industry were presented and discussed. This special issue highlights a selection of 12 manuscripts from oral presentations and poster contributions.

Glycolytic Functions Are Conserved in the Genome of the Wine Yeast Hanseniaspora uvarum, and Pyruvate Kinase Limits Its Capacity for Alcoholic Fermentation.

Hanseniaspora uvarum (anamorph Kloeckera apiculata) is a predominant yeast on wine grapes and other fruits and has a strong influence on wine quality, even when Saccharomyces cerevisiae starter cultures are employed. In this work, we sequenced and annotated approximately 93% of the H. uvarum genome. Southern and synteny analyses were employed to construct a map of the seven chromosomes present in a type strain. Comparative determinations of specific enzyme activities within the fermentative pathway in H. uvarum and S. cerevisiae indicated that the reduced capacity of the former yeast for ethanol production is caused primarily by an ∼10-fold-lower activity of the key glycolytic enzyme pyruvate kinase. The heterologous expression of the encoding gene, H. uvarumPYK1 (HuPYK1), and two genes encoding the phosphofructokinase subunits, HuPFK1 and HuPFK2, in the respective deletion mutants of S. cerevisiae confirmed their functional homology.IMPORTANCEHanseniaspora uvarum is a predominant yeast species on grapes and other fruits. It contributes significantly to the production of desired as well as unfavorable aroma compounds and thus determines the quality of the final product, especially wine. Despite this obvious importance, knowledge on its genetics is scarce. As a basis for targeted metabolic modifications, here we provide the results of a genomic sequencing approach, including the annotation of 3,010 protein-encoding genes, e.g., those encoding the entire sugar fermentation pathway, key components of stress response signaling pathways, and enzymes catalyzing the production of aroma compounds. Comparative analyses suggest that the low fermentative capacity of H. uvarum compared to that of Saccharomyces cerevisiae can be attributed to low pyruvate kinase activity. The data reported here are expected to aid in establishing H. uvarum as a non-Saccharomyces yeast in starter cultures for wine and cider fermentations.

Persistence of Two Non-Saccharomyces Yeasts (Hanseniaspora and Starmerella) in the Cellar.

Different genera and/or species of yeasts present on grape berries, in musts and wines are widely described. Nevertheless, the community of non-Saccharomyces yeasts present in the cellar is still given little attention. Thus it is not known if the cellar is a real ecological niche for these yeasts or if it is merely a transient habitat for populations brought in by grape berries during the winemaking period. This study focused on three species of non-Saccharomyces yeasts commonly encountered during vinification: Starmerella bacillaris (synonymy with Candida zemplinina), Hanseniaspora guilliermondii and Hanseniaspora uvarum. More than 1200 isolates were identified at the strain level by FT-IR spectroscopy (207 different FTIR strain pattern). Only a small proportion of non-Saccharomyces yeasts present in musts came directly from grape berries for the three species studied. Some strains were found in the must in two consecutive years and some of them were also found in the cellar environment before the arrival of the harvest of second vintage. This study demonstrates for the first time the persistence of non-Saccharomyces yeast strains from year to year in the cellar. Sulfur dioxide can affect yeast populations in the must and therefore their persistence in the cellar environment.

FT-IR spectroscopy: A powerful tool for studying the inter- and intraspecific biodiversity of cultivable non-Saccharomyces yeasts isolated from grape must.

The efficiency of the FT-IR technique for studying the inter- and intra biodiversity of cultivable non-Saccharomyces yeasts (NS) present in different must samples was examined. In first, the capacity of the technique FT-IR to study the global diversity of a given sample was compared to the pyrosequencing method, used as a reference technique. Seven different genera (Aureobasidium, Candida, Cryptococcus, Hanseniaspora, Issatchenkia, Metschnikowia and Pichia) were identified by FT-IR and also by pyrosequencing. Thirty-eight other genera were identified by pyrosequencing, but together they represented less than 6% of the average total population of 6 musts. Among the species identified, some of them present organoleptic potentials in winemaking, particularly Starmerella bacillaris (synonym Candidazemplinina). So in a second time, we evaluated the capacity of the FT-IR technique to discriminate the isolates of this species because few techniques were able to study intraspecific NS yeast biodiversity. The results obtained were validated by using a classic method as ITS sequencing. Biodiversity at strain level was high: 19 different strains were identified from 58 isolates. So, FT-IR spectroscopy seems to be an accurate and reliable method for identifying major genera present in the musts. The two biggest advantages of the FT-IR are the capacity to characterize intraspecific biodiversity of non-Saccharomyces yeasts and the possibility to discriminate a lot of strains.

Diversity of yeast strains of the genus Hanseniaspora in the winery environment: What is their involvement in grape must fermentation?

Isolated yeast populations of Chardonnay grape must during spontaneous fermentation were compared to those isolated on grape berries and in a winery environment before the arrival of the harvest (air, floor, winery equipment) and in the air through time. Two genera of yeast, Hanseniaspora and Saccharomyces, were isolated in grape must and in the winery environment before the arrival of the harvest but not on grape berries. The genus Hanseniaspora represented 27% of isolates in the must and 35% of isolates in the winery environment. The isolates of these two species were discriminated at the strain level by Fourier transform infrared spectroscopy. The diversity of these strains observed in the winery environment (26 strains) and in must (12 strains) was considerable. 58% of the yeasts of the genus Hanseniaspora isolated in the must corresponded to strains present in the winery before the arrival of the harvest. Although the proportion and number of strains of the genus Hanseniaspora decreased during fermentation, some strains, all from the winery environment, subsisted up to 5% ethanol content. This is the first time that the implantation in grape must of populations present in the winery environment has been demonstrated for a non-Saccharomyces genus.

Phytotoxic chaetoglobosins are produced by the plant pathogen Calonectria morganii (anamorph Cylindrocladium scoparium).

By the application of a bioassay based on cresson seedlings, two phytotoxic compounds were isolated by thin-layer chromatography from the culture fluid of a Calonectria morganii isolate. The structure of both compounds was elucidated by ESI/MS and NMR spectroscopy. According to the Chemical Abstracts database, they were identified as chaetoglobosin A and 19-O-acetylchaetoglobosin A, mycotoxins originally described for Chaetomium globosum.